There is an image forming apparatus that form an image on a sheet with decolorizable material. When the image formed on the sheet with the decolorizable material is subjected to an erasing process by heating the sheet to a certain temperature, the image is erased and the sheet can be reused for printing. Thus, the same sheet can be repetitively used. In addition, a conventional image forming apparatus that forms an image on a sheet with a non-decolorizable material is known. When it is desired to form the image of the decolorizable material and the image of the non-decolorizable material on a single sheet, these images are formed separately on the sheet.